This project will combine the efforts of research groups at Cornell, the Technical University of Munich, and at the Wadsworth Center to quantify and statistically model associations between clonal Listeria monocytogenes groups and different environments and hosts. An independently funded parallel study in China will allow us to evaluate whether patterns and associations in the US are broadly applicable. Preliminary results show (i) that clonal L. monocytogenes groups differ in their likelihood to cause human and animal disease and (ii) that L. monocytogenes virulence genes appear to also be functionally important outside mammalian hosts (e.g., for interactions with protozoan cells). Laboratory studies will characterize phenotypes of clonal subgroups associated with specific environments or host species to determine the biological relevance of associations among clonal L. monocytogenes groups and different habitats. Laboratory studies will also define specific habitats (including non-mammalian host species) that may provide selective pressures for maintenance of virulence genes and the emergence of new L. monocytogenes strains. The outcome of this project will be a model of transmission dynamics of Listeria clonal groups and of environmental, host, and agent factors affecting transmission dynamics. Our studies will define environments likely to significantly and directly affect Listeria transmission dynamics when influenced by anthropogenic changes. The specific objectives of our study are: 1. Determine the distribution of clonal L. monocytogenes groups among (i) human hosts; (ii) non-primate mammalian hosts; and (iii) non-host related environments using culturing techniques and molecular and phenotypic approaches for characterization of isolates. 2. In parallel to Objective 1, use non-culturing-based techniques to determine the distribution of L. monocytogenes clonal groups in different environments using molecular approaches to avoid culturing bias. 3. Determine associations between L. monocytogenes clonal groups and different environments and host species and develop a transmission model for different clonal groups. 4. Determine the phenotypes of L. monocytogenes clonal groups associated with specific environments and hosts and determine the genetic basis for phenotypes associated with a preference for specific habitats.